1986 Jaguar XJS petrol gauge

DPUNCH

1986 JAGUAR XJS

1986 Jaguar XJS V12 Two Wheel Drive Automatic 80000 miles

I have just bought a bove & petrol gauge registering empty no matter how much fuel. Previous owner says this happened before spontaneously and then rectified itself.
Is this a blockage of some kind causing this?
Thanking you.